In recent years, the Global Positioning System (GPS) has provided a significant advancement in satellite communications. Individuals engaged in outdoor activities are major users of the GPS system, and they typically make use of hand held receivers to provide positional information. The receiver that is required in order to efficiently utilize the GPS satellite signals includes an antenna that must provide a right hand circular polarization and a uniform pattern coverage over virtually all of the upper hemisphere. By providing a uniform amplitude response over a wide coverage region, the receiver is able to maintain a signal lock to the GPS satellites with a useful signal to noise ratio.
Slot antennas have been developed and used in GPS applications, largely in recognition of the characteristics that GPS antennas must exhibit in order to effectively use the GPS system to provide accurate positional data. A variety of slotted antennas have been proposed, including cylindrical slot antennas that are provided with helical slots. The prior antennas have included four slots and have generally been described as a quadrifilar slot antennas that have used micro strip feed systems. This type of antenna has been found to be generally satisfactory in many applications, and it is characterized by a number of positive attributes, including the ability to produce broad beam patterns, simple feeding and matching techniques, suitability for mass production, and a lightweight and compact construction. However, cylindrical slot antennas have suffered from relatively poor coverage near the horizon and from multi-path shortcomings.